The present invention relates to a recording apparatus that has an endless recording function by which high-speed, large-volume digital data represented by real-time stream data such as video data and audio data is recorded endlessly and a prealert recording function by which when an alert signal indicating some kind of abnormality has been detected during endless recording, data before and after the alert signal detecting timing is stored.
Along with increasing processing speed of processors and decreasing prices of memories and secondary recording media, there is a growing demand for recording apparatuses that can record high-speed, large-volume digital data represented by real-time stream data such as video data and audio data. There is also a growing demand for recording apparatuses adapted for monitoring applications. That is, for the security of automatic teller machines and factories, there is a growing demand for recording apparatuses that have an endless recording function by which monitoring data is recorded endlessly and a prealert recording function by which when an alert signal indicating some kind of abnormality has been detected during endless recording, data before and after the alert signal detecting timing is stored.
A conventional recording apparatus will hereunder be described with reference to the drawings. FIG. 5 is a diagram showing a configuration of a conventional recording apparatus. In FIG. 5, reference numeral 401 denotes an input section that inputs data; 402, a first recording section that has an endless magnetic tape as a recording medium and records data onto the magnetic tape; 403, a buffer section that temporarily stores data for a predetermined time period; 404, a second recording section that has a non-endless magnetic tape as a recording medium and records data onto such magnetic tape; 405, a control section that controls data transfer between the input section 401 and the first recording section 402, between the input section 401 and the buffer section 403, and between the buffer section 403 and the second recording section 404. Further, reference numerals 406-1, 406-2, . . . , . . . , 406-n denote analog video and audio input units that input analog video data and analog audio data; 407, an analog video and audio input switching unit that controls the inputting of analog video data and analog audio data; 408, a video data analog-to-digital converting unit that digitizes analog video data; 409, an audio data analog-to-digital converting unit that digitizes analog audio data; 410, a digital video data compressing unit that compresses digital video data; 411, a digital audio data compressing unit that compresses digital audio data; and 412, a compressed digital video and audio data multiplexing unit that multiplexes digital compressed video data and digital compressed audio data. These components constitute the input section 401.
An operation of the thus configured recording apparatus will be described with reference to FIG. 6. FIG. 6 is a diagram showing a process flow of the control section. First, the control section 405 starts simultaneous data transfer between the input section 401 and the first recording section 402 and between the input section 401 and the buffer section 403 (step 502). This data transfer operation is continuously performed until data recording is ended. During this operation, in the first recording section 402, data is repetitively recorded onto the endless magnetic tape. In the buffer section 403, the data is repetitively recorded in a ring buffer.
Here, a flow of data in the input section 401 will be described. The analog video and audio input units 406-1, 406-2, . . . , . . . , 406-n output analog video data and analog audio data to the analog video and audio input switching unit 407, respectively. The analog video and audio input switching unit 407 switches the analog video and audio input unit at a predetermined time interval while instructed by the control section 405, so that analog video data and analog audio data to be recorded are switched. The video data analog-to-digital converting unit 408 subjects the analog video data switched by the analog video and audio input switching unit 407 to an analog-to-digital conversion process, and delivers the digital video data to the digital video data compressing unit 410. The digital video data compressing unit 410 compresses the digital video data delivered from the video data analog-to-digital converting unit 408, and delivers digital compressed video data to the digital compressed video and audio data multiplexing unit 412. On the other hand, the audio data analog-to-digital converting unit 409 subjects the analog audio data switched by the analog video and audio input switching unit 407 to an analog-to-digital conversion process, and delivers digital audio data to the digital audio data compressing unit 411.
The digital audio data compressing unit 411 compresses the digital audio data delivered from the audio data analog-to-digital converting unit 409, and delivers digital compressed audio data to the digital compressed video and audio data multiplexing unit 412. Further, the digital compressed video and audio data multiplexing unit 412 multiplexes the digital compressed video data delivered from the digital video data compressing unit 410 and the digital compressed audio data delivered from the digital audio data compressing unit 411, and outputs stream data.
Then, in step 503, the control section 405 detects an alert signal outputted from the analog video and audio input units 406-1, 406-2, . . . , . . . , 406-n. If no alert signal has been detected, the control section 405 advances to step 505. If an alert signal has been detected, the control section 405 transfers data between the buffer section 403 and the second recording section 404 for a predetermined time period (step 504), and advances to step 505. In step 504, by recording data already stored in the buffer section 403 at the alert signal detecting timing, not only data corresponding to the capacity of the buffer section before the alert signal detecting timing can be recorded, but also data corresponding to a predetermined time after the alert signal detecting timing can be recorded. Finally, in step 505, if an endless recording end instruction is not given, the control section 405 returns to step 503 to repeat the above operation. If an endless recording end instruction has been given, the control section 405 ends the operation (step 506).
However, in the conventional recording apparatus, in order to implement the endless recording function and prealert recording function for video data and audio data in the video and audio input unit of the input section, the video data and the audio data in the video and audio input unit are repetitively recorded onto the endless magnetic tape of the first recording section and the buffer section during endless recording, and when an alert signal has been detected, the video data and the audio data stored in the buffer before and after the alert signal detecting timing is recorded onto the magnetic tape of the second recording section. Therefore, two recording sections must be arranged, which in turn has imposed the problem that the recording apparatus becomes expensive. In addition, the data is recorded onto magnetic tapes, which in turn has imposed the problem that much time is entailed in searching data after recording.